Underlapping sheet feeders

ABSTRACT

A sheet feeder comprises a roller configured to rotate about an axis and an input drive configured to deliver single sheets to the roller such that a leading edge of each sheet is substantially parallel to the axis. The roller comprises a plurality of flexible fins extending along the axis. As the roller rotates, one of the sheets can be lifted by the rotating fins to pass over the roller, while the leading edge of a following sheet is delivered to the roller in an underlapping relationship with the first sheet.

TECHNICAL FIELD

The invention relates to the arrangement of sheets of paper, card or other thin material into a line in which each sheet underlaps the preceding sheet. In other words, the leading edge of each sheet lies underneath the preceding sheet. Typically the incoming sheets are delivered singly, e.g. from the bottom of a stack, and the line of outgoing sheets is fed into a machine for further processes such as folding, printing or laminating to be carried out.

BACKGROUND OF THE INVENTION

In the prior art, when it was desired to form a series of sheets or other thin articles into an underlapping line, this was typically achieved using suction cups to lift the preceding sheet, or using complicated reciprocating mechanisms to control the edges of the sheets. A simpler solution is desirable.

SUMMARY OF THE INVENTION

The invention provides a sheet feeder as defined in claim 1.

The invention further provide a method of feeding sheets in an underlapping series as defined in claim 7.

Other features of the invention that are preferred but not essential are defined in the dependent claims.

THE DRAWINGS

FIG. 1 is a vertical cross section through a sheet feeder according to an embodiment of the invention.

FIG. 2 is a series of schematic drawings showing the sequence of steps as sheets pass through a feeder according to the invention.

FIG. 1 shows a sheet feeder that draws sheets from the underside of a stack 2 of paper, card or other thin material to be processed. The stack 2 rests on a feed deck 4. The feed deck 4 is preferably inclined from the horizontal and the stack 2 is restrained from moving under gravity by a feed block 6, against which the leading face of the stack 2 rests. A small gap between the feed block 6 and the feed deck 4 permits one sheet at a time to be withdrawn from the bottom of the stack 2 and to pass through the gap. A moving belt 8 set into the feed deck 4 frictionally engages the underside of the bottom sheet and drives it through the gap towards a roller 10.

The details of the feed deck 4, feed block 6 and drive belt 8 are conventional and do not form part of the present invention. Alternative means for supplying the sheets could be used; all that is important is that single sheets are driven one at a time towards the roller 10 along a direction that is substantially perpendicular to the axis. Note that this does not mean that the delivery direction necessarily points directly towards the axis; preferably it is aligned above the axis. In the typical case of rectangular sheets, the leading edge of each sheet will be aligned substantially parallel to the axis of the roller.

The roller 10 is mounted for rotation about a horizontal axis. A number of fins 12 are spaced equally about the circumference of the roller. There are five of the fins 12 in this example. The fins 12 extend along the roller 10, generally parallel to its axis, and radiate out from the surface of the roller. Each fin 12 preferably curves backwards with respect to the direction of rotation of the roller 10. It is not essential that the roller 10 or the fins 12 should extend across the whole width of the feeder. Two or more rollers 10 of reduced width, each with its own set of fins 12, could be spaced along a single axle. Alternatively, a single, full-width roller 10 could support two or more sets of fins 12 of reduced width. The fins 12 may be formed integrally with the roller 10 or they may be attached to it. The latter option gives the advantage of an independent choice of their material at the expense of a more complex manufacturing process. The fins 12 are flexible and yielding to avoid damage to the sheets and to permit the “flicking” action described below. They may be made of a material such as rubber that can grip the sheets and help to guide them over the roller 10 as it rotates.

Downstream from the roller 10 is an output platen 14 for receiving the underlapping series of sheets. As shown, the output platen 14 is not necessarily aligned with the input feed deck 4 and preferably it extends beneath the roller 10. The platen 14 may be the table of a laminator or other machine supplied by the sheet feeder. A gate 18 is provided to act as a barrier that selectively blocks the movement of a sheet away from the roller 10 as explained below. The gate 18 may comprise one or more teeth that can be raised through slots in the platen 14. Other known forms of gate may be used with the invention.

An output drive 16 may be associated with the output platen 14 for drawing the series of sheets away from the roller 10 and along the output platen 14 towards the next stage of the process, such as a laminating machine. In the illustrated embodiment the output drive comprises a pair of spaced rollers 16,17. When the gate 18 is lowered to allow a sheet to pass, the upper roller 16 is simultaneously lowered so that the sheet becomes sandwiched between the upper and rollers 16,17. At least one roller of the pair is driven so that the sheet is urged downstream between the counter-rotating rollers 16,17. Other forms of output drive synchronized with the gate 18 are possible. In some applications, an inclined output platen 14 may be sufficient to move the outgoing sheets under the influence of gravity, without any additional output drive.

FIG. 2 illustrates the operation of the invention. In this case, successive sheets 21,22,23 are shown advancing singly along the feed deck 4 instead of being withdrawn from the underside of a stack. This is for ease of understanding but is also a possibility falling within the scope of the invention. For simplicity, the input and output drives are not shown in the diagrams of FIG. 2.

FIG. 2(a) shows a first sheet 21 advancing along the feed deck 4 towards the roller 10.

The first sheet 21 is followed, after a small gap, by a second sheet 22. The gap is determined by the timing of the upstream supply mechanism and is not essential. The plane of the feed deck 4 is preferably aligned just above the axis of the roller 10 so that the leading edge of the first sheet 21 is directed towards the upper half of the roller 10. As shown, the leading edge enters the space between two of the fins 12.

The roller 10 is continuously rotated at a rate such that a surface speed of the roller 10 is faster than the speed at which the sheet 21 is delivered. Thus the fins 12 move faster than the leading edge of the sheet 21 and do not block the forward progress of the sheet. The front edge 24 of the feed deck 4 preferably lies just within the sweep of the fins 12 so that as the roller 10 rotates, the outer ends of the fins 12 catch against the edge 24. Being flexible, each fin 12 is then bent backwards until its tip has passed the edge 24 and, being resilient, the fin 12 then flicks forwards to resume its original shape. This arrangement closes the gap between the edge 24 of the feed deck and the fins 12 most of the time and thus prevents the leading edge of the sheet 21 passing below the roller 10. It also imparts a rapid, upward movement to the tip of the fin 12 as it flicks forwards, which helps to lift the sheet 21 over the roller 10 as discussed below.

FIG. 2(b) shows an instant shortly after FIG. 2(a), when the continuing rotation of the roller 10 has brought one of the fins 12 past the edge 24 of the feed deck, into contact with the underside of the first sheet 21, and the fin has lifted the sheet 21 clear of the top of the roller 10. The sheet 21 is still moving forwards at the speed determined by the input drive, which continues to act on the rear part of the sheet 21 on the feed deck 4. Meanwhile, the roller 10 is rotating at a sufficiently high speed such that successive fins 12 sweep past the underside of the sheet 21 and maintain its elevated position.

FIG. 2(c) shows a further progression, as the first sheet 21 has moved further across the top of the roller 10 until its trailing edge ceases to be acted on by the input drive and its leading edge begins to be acted on by the output drive. Friction between the rotating fins 12 and the underside of the sheet 21 can help to keep the sheet moving forwards during this transition.

In FIG. 2(d), the further progress of the first sheet 21 away from the roller 10 is blocked by the gate 18, which obstructs its leading edge. Alternatively (or additionally) the movement of the sheet 21 may be stopped by interrupting the operation of the output drive. Thus the first sheet 21 is stationary above the roller 10, supported on the rotating fins 12. Meanwhile, the second sheet 22 has advanced to the position that the first sheet 21 adopted in FIG. 2(a), with its leading edge approaching the roller 10 and penetrating the space between two of the fins 12. A third sheet 23 now follows the second sheet 22 along the feed deck 4.

In FIG. 2(e), a few moments later, the second sheet 22 has been lifted by the continuing rotation of the fins 12 to be supported on the rotating fins above the top of the roller 10. The position of the second sheet 22 in FIG. 2(e) is the same as the position of the first sheet 21 in FIG. 2(b), except that the first sheet 21 is already present. Thus the leading edge of the second sheet 22 now lies below the trailing part of the first sheet 21 in an underlapping relationship. The system may determine when a sufficient degree of underlap has been achieved either by the time that has passed since the first sheet 21 was stopped by the gate 18 or, preferably, by using a sensor (not shown) to detect that the second sheet 22 has reached the desired position. The gate 18 can then be de-activated and/or the output drive can be restarted to drive the first sheet 21 away from the roller 10 at the same speed as the second sheet 22 is driven towards it, thus maintaining the desired amount of underlap.

It should be evident that the cycle of steps illustrated and described with respect to FIGS. 2(c)-(e) can be repeated indefinitely, to underlap the third sheet 23 with the second sheet 22 and so on.

Instead of operating the output drive at the same speed as the input drive, but intermittently, it is also possible to operate the output drive continuously at a slower speed, which will be equal to its average speed in the first embodiment of the invention just described. In the first embodiment, the first sheet 21 stops to wait for the second sheet 22 to catch up. In this alternative embodiment the second sheet 22 will overtake (and underlap) the first sheet 21 more gradually, based on the difference in speed between them, but the outcome will be the same. It will in any case be necessary that the output series of overlapping sheets should move at this slower speed by the time it reaches the input of the following process if it is a continuous one.

The number of fins 12 may be selected depending on the application, the nature of the sheets to be processed and the speed of the roller 10. With fewer fins 12, it is likely that the roller 10 will need to be rotated faster to achieve the desired effect. As discussed above, the minimum rate of rotation is determined by the need for the surface speed of the roller to exceed the delivery speed of the sheets. Thus at least three fins are likely to be required for the roller to be effective. There is unlikely to be any benefit in the number of fins exceeding ten; a larger number of fins will allow less time for the leading edge of a sheet to penetrate between them before the next fin contacts the sheet and lifts it.

The roller 10 may be independently driven by its own motor (not shown). Preferably it is driven at an appropriate speed by gearing linking it to the input drive. The roller 10 will normally rotate continuously, as previously described but intermittent operation of the roller, timed in relation to the operation of the gate 18 and/or the drive means 8, may also be possible. 

1.-12. (canceled)
 13. A sheet feeder comprising: a roller configured to rotate about an axis; and an input drive configured to deliver single sheets to the roller along a direction substantially perpendicular to the axis; wherein the roller comprises a plurality of flexible fins extending along the axis, whereby as the roller rotates a first one of the sheets can be lifted by the fins to pass over the roller and a leading edge of a second one of the sheets can be delivered to the roller in an underlapping relationship with the first sheet.
 14. A sheet feeder according to claim 13, comprising at least three fins disposed about the circumference of the roller.
 15. A sheet feeder according to claim 13, comprising up to ten fins disposed about the circumference of the roller.
 16. A sheet feeder according to claim 13, wherein the input drive delivers the sheets along the surface of a platen, an edge of the platen being positioned to come into contact with the fins during rotation of the roller.
 17. A sheet feeder according to claim 13, further comprising an output drive configured to withdraw sheets from the roller.
 18. A sheet feeder according to claim 13, further comprising a gate for controlling the withdrawal of sheets from the roller.
 19. A method of feeding sheets in an underlapping series, comprising: delivering a series of single sheets to a roller, the roller comprising a plurality of flexible fins extending along an axis of the roller and the sheets being delivered along a direction substantially perpendicular to the axis; rotating the roller so that the fins lift a first one of the sheets to pass over the roller; delivering a second one of the sheets to the roller while the first sheet remains above the roller; and rotating the roller so that the fins lift the second sheet to pass over the roller in an underlapping relationship with the first sheet.
 20. A method according to claim 19, comprising rotating the roller continuously.
 21. A method according to claim 20, comprising rotating the roller at a rate such that a surface speed of the roller is faster than a delivery speed of the sheets.
 22. A method according to claim 19, comprising using a gate downstream from the roller to maintain the first sheet above the roller while the second sheet is delivered to the roller.
 23. A method according to claim 19, comprising operating an output drive to withdraw the sheets from the roller.
 24. A method according to claim 19, further comprising aligning the sheets such that they are delivered to the roller with a leading edge of each sheet substantially parallel to the axis. 